Using common method 'bool_from_string' from oslo strutils

Using common method 'bool_from_string' from oslo strutils to replace
utils.string_to_bool.

partially implements blueprint common-client-library-2

Change-Id: I22ee9c5a4b48e85606e033ab87d4adb72b665ee6
Merge "Using common method 'bool_from_string' from oslo strutils"